I'm not saying that it didn't happen, I think that it did, but it is harder to prove that it did. There are a lot of other reasons that the money could have been held up, and regardless of how credible they are, or aren't, the Republicans will hold them up as the "real reason" it was delayed. Also there is no absolute proof that it was, rather a lot of circumstantial evidence pointing towards it, and a lot of people believing it was held up because of that.
Whereas with the WH Meeting, there are none of those issues. It was held up and never given, there are a lot of people saying that the investigations were absolutely required for getting that meeting. The Ukrainians knew that to get the WH Meeting they had to announce the investigations, and there was a lot of work that was done to get a statement done, and there is no argument that the requirements for the WH Meeting were directly attributable to Trump.
The hold on the aid might be the "worst" of the two offences, but the case for the Meeting is the far stronger of the two.